The present invention relates to optical head driving device, and more specifically relates to particular optical head driving device of the type in which information is recorded onto a surface of recording medium disk by optical means, and recorded information is read out or erased. Further, the present invention relates to particular optical head driving device in which an optical head is driven by a voice coil motor in an optical disk apparatus operative to record information on a face of recording medium disk by optical means and to read out or erase the recorded information.
Generally, the optical disk apparatus has a spindle for mounting and rotating a recording medium of circular or disk shape (optical disk), and an optical head operative to record binary information sequentially along recording tracks formed substantially concentrically on the recording medium surface while rotating the recording medium by the spindle. Readout and erase of the recorded information are effected sequentially by the optical head while rotating the optical disk in similar manner. The optical head is driven in the radius direction relative to the optical disk by means of a driving device. By such construction, recording, reading out and erasing of information are carried out over the entire face of optical disk.
Such type of the optical disk apparatuses includes one type for especially carrying out high speed information processing which has an optical head driving unit comprised of a voice coil motor provided with a driving coil, in a fixed magnetic circuit, connected to the optical head. This type of the high speed optical disk apparatus can drive (access) the optical head at far faster than that utilizing other driving unit such as stepping motor.
Conventionally, in this type of the optical head driving unit of optical disk apparatus having the voice coil motor as driving source, the driving unit is disposed at one side of the optical head with respect to the moving direction of the optical head, or disposed oppositely to the spindle. Further, the spindle and the fixed magnetic circuit of the voice coil motor are mounted independently of each other on a base plate.
However, in the above described conventional optical head driving device in which the driving unit is disposed at one side of the optical head, since the direction of driving force must coincide to the moving direction of the optical head, the action point of the driving force is not coincident with the center of gravity of the movable optical head, thereby causing drawback that unnecessary vibration is generated during the driving. In order to eliminate such drawback, the driving unit may be disposed on both sides of the optical head so as to balance the driving force. However, it is quite difficult to maintain the balance in vast number of individual optical disk apparatuses without fluctuation of balance. Moreover, the driving force is transmitted to the optical head through a kind of beam structure perpendicular to the action direction thereof, hence there is caused another drawback that sufficiently high driving performance and high tracking performance cannot be obtained. Further, such structure is complicated, thereby causing additional drawback such as low productivity and high cost.
On the other hand, in the optical head driving device of the type in which the driving unit is disposed in opposed relation to the spindle with respect to the optical head (U.S. Pat. No. 4,190,860), the structure is simple and the driving force is efficiently transmitted. However, the driving unit has an elongated shape protruding considerably out of the periphery of the optical disk in the moving direction of the optical head, hence it has drawback that the entire length of the optical head driving device is extended. Further, in such structure, the spindle, optical head, guide member for movement of the optical head and driving unit are aligned linearly in series such that the spindle and the driving unit are fixed on the base in farmost positions separated from each other. Accordingly, in order to suppress unnecessary resonance, sufficiently high rigidity is needed for the base. However, a small size of the apparatus cannot use highly rigid base due to lack of space, thereby causing drawback that the spindle is vibrated relative to the optical head.